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https://www.swift.org

Performance

· 16 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
91
GRADE
A
FIX
1
REVIEW
2
PASS
11
INFO
2

Performance-focused optimization plan with CWV assessment, top offenders, and time estimates

Mobile Desktop
44
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
100
Accessibility Measures how accessible the page is for users with disabilities. Checks color contrast, ARIA labels, and semantic HTML.
100
Best Practices Checks for modern web development best practices including HTTPS, no console errors, and secure JavaScript.
92
SEO Measures basic SEO optimizations: meta tags, crawlability, link text, and mobile friendliness.

First Contentful Paint First Contentful Paint — how long until the browser renders the first piece of content. Under 1.8s is good.

3.32 s

Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.

6.26 s

Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.

1.35 s

Cumulative Layout Shift Cumulative Layout Shift — measures visual stability. How much the page layout shifts during loading. Under 0.1 is good.

0.000

Speed Index Speed Index — how quickly content is visually displayed during load. Under 3.4s is good.

4.37 s

Time to Interactive Time to Interactive — how long until the page is fully interactive and responds to user input. Under 3.8s is good.

6.64 s

Page Load Progression

375 ms
750 ms
1.1 s
1.5 s
1.9 s
2.2 s
2.6 s
3.0 s
Checks
16
11 PASS 2 REVIEW 1 FIX
D
JS Execution Cost
Action
3233ms total JS execution
FIX
3233ms total JS execution
Warning::
https://www.swift.org/assets/javascripts/new-javas...: 2730ms CPU time
Info::
https://www.swift.org/assets/javascripts/new-javas...: 214ms CPU time
Info::
Unattributable: 204ms CPU time
Info::
https://www.swift.org/: 85ms CPU time
Info::
Third-party scripts: 204ms (6% of total)

Main Thread Breakdown

Other 83% Script Evaluation 10% Style & Layout 5%
ScriptTotalScriptingParse/CompileParty
https://www.swift.org/assets/javascripts/new-javascripts/vendor/anime.iife.min.js2730ms150ms9ms1st
https://www.swift.org/assets/javascripts/new-javascripts/hero.js214ms86ms1ms1st
Unattributable204ms5ms0ms3rd
https://www.swift.org/85ms31ms2ms1st
B
Image Optimization
16 images, 0 KB saveable
REVIEW
16 images, 0 KB saveable
Info::
All images are well-optimized
16 images 21 KB
0 oversized -0 KB
10 legacy format
0 missing dimensions CLS risk
C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A+
Page Weight Budget
657 KB transferred, 32 requests
PASS
657 KB transferred, 32 requests
Info::
Page weighs 722 KB (657 KB transferred)
Info::
32 HTTP requests
Info::
Estimated 0.13 g CO2 per page load
657 KB / 2.4 MB budget
657 KB transferred
32 requests
0.13 g CO2 per page load
Other 431.4 KiB 66%
JavaScript 179.4 KiB 27%
Images 20.7 KiB 3%
CSS 16.5 KiB 3%
HTML 9.3 KiB 1%
0 2.4 MB 4.9 MB
Under budget
A+
Third-Party Impact
13% third-party, 0 ms blocking
PASS
13% third-party, 0 ms blocking
Info::
Third-party code accounts for 13% of page weight (84.7 KiB of 657.3 KiB)
Info::
Third-party blocking time is low (0 ms)
87%
First-party Third-party
A+
Text Compression
All text resources are compressed
PASS
All text resources are compressed
Info::
All text resources are compressed
All text resources are properly compressed.
A+
Font Loading
No web fonts (system fonts)
PASS
No web fonts (system fonts)
Info::
No web fonts loaded — system fonts are fastest
No web fonts loaded — system fonts are optimal.
A
JS Bundles
6 scripts, 45 KB unused
PASS
6 scripts, 45 KB unused
Warning::
https://www.swift.org/assets/javascripts/new-javas...: 45 KB unused (60%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.swift.org/assets/javascripts/new-javas...: unminified — 3 KB could be saved
Info::
Total unused JavaScript: 45 KB
45 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.swift.org/assets/javascripts/new-javascripts/vendor/anime.iife.min.js75 KB45 KB (60%)✓1st
https://www.swift.org/assets/javascripts/new-javascripts/color-scheme-toggle.js4 KB—✓1st
https://www.swift.org/assets/javascripts/new-javascripts/hero.js9 KB—✗1st
https://www.swift.org/assets/javascripts/new-javascripts/application.js7 KB—✓1st
https://www.swift.org/assets/javascripts/new-javascripts/landing.js2 KB—✓1st
https://developer.apple.com/assets/metrics/scripts/analytics.js83 KB—✗3rd

Consider code splitting or tree shaking to reduce unused code.

Why this matters

This bundle has high unused code — code-split or tree-shake to ship only what executes.

Source: web.dev / Lighthouse coverage

A+
Resource Caching
All resources properly cached
PASS
All resources properly cached
Info::
No caching issues found
All static resources have appropriate caching headers.
A+
Critical Rendering Path
No render-blocking resources
PASS
No render-blocking resources
Info::
No render-blocking resources detected
A+
Resource Hints
6 hints, 0 missing preconnects
PASS
6 hints, 0 missing preconnects
Info::
Page uses 6 resource hint(s)

Current Resource Hints

preconnect
—
preload
—
dns-prefetch
—
prefetch
6

6 resource hints configured

A+
Render-Blocking Resources
No render-blocking resources detected
PASS
No render-blocking resources detected
Info::
No render-blocking resources detected in <head>
A+
Third-Party Resources
No third-party resources detected
PASS
No third-party resources detected
A+
HTTP Caching
max-age=180 (3 minutes)
PASS
max-age=180 (3 minutes)
Info::
Cache-Control header is set
Got: max-age=180, public
Info::
Effective TTL: 3 minutes (max-age=180)
Info::
ETag present — enables conditional (304) responses
Info::
Last-Modified header present
Cache-Control

max-age=180, public

DirectiveValueMeaning
max-age180Cache for 3 minutes
public—Any cache may store this response
Effective TTL: 180 seconds
Network Waterfall
32 requests over 0ms
INFO

Performance analysis not available for this result.

Third-Party Script Cost
Per-script blocking time, transfer cost, and cache headers
INFO
6% of JavaScript execution is third-party
First-party Third-party 204ms · 0KB · $3/mo
Unattributable
Other
Costly
Execution 204ms
Transfer 0 KB
Monthly Cost $3/mo

These scripts may cost more than they're worth

  • Unattributable adds 204ms and costs ~$3/month

Unattributable takes 204ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.

Why this matters

This script has high main-thread execution time — optimize hot paths or defer.

Source: web.dev

How third-party costs are calculated

All checks on this page are automated. Results are estimates - run targeted manual reviews when the score affects a release decision.

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